Development of an evanescent optical integrated sensor in the mid-infrared for detection of pollution in groundwater or seawater

Abstract

The detection of molecules dissolved in liquid medium can be envisaged by means of an optical integrated sensor operating in middle infrared range. The intended sensor is composed of a cladding and a guiding selenide sputtered layers transparent in middle infrared. Hence, Ge-Sb-Se thin films were selected in view of tailored refractive index contrast, successfully deposited by radio frequency magnetron sputtering and characterized. To maximize the evanescent field at a wavelength of 7.7 µm, a suitable selenide waveguide allowing measuring the optical transmitted power was designed by performing computer simulations based on the effective index method enabling single-mode propagation for a waveguide width between 8 and 12 µm. Selenide sputtered films were micro-patterned using reactive ion etching with inductively coupled plasma process. Finally, optical waveguide surface was functionalized by the deposition of a hydrophobic polymer, which will permit detection of organic molecules in water.

Keywords:

• Optical sensing and sensors
• mid-infrared
• integrated optics devices
• Chalcogenide glasses
• thin films